1. Field of the Invention
This invention relates to automatic cleaning machines for cleaning reusable foodstuff containers, and more particularly, to apparatus for supplying and circulating liquid in machines of the type having successive liquid cleaning or rinsing baths or stages for application of cleaning agent and rinse to foodstuff containers.
2. Description of the Prior Art
For the cleaning of reusable foodstuff containers of all kinds, such as bottles, cans or other metal parts, automatic cleaning machines are employed. In such machines, the generally cold container stock to be cleaned is treated in several stages and/or baths at selected temperatures and with suitable concentration of cleaning agents. Generally, these stages include a preliminary cleaning stage, a main cleaning stage and a subsequent rinsing stage.
The temperatures, the types of chemical cleaning agents used and their concentration may vary between the different stages. The rinsing stage is usually carried out by rinsing the container stock in clean water. When cleaning containers subsequently to be used for foodstuffs, fresh water is principally used for the last rinsing stage in the cleaning process. The fresh water supplied to the cleaning machine, after being used in various other individual stages of the cleaning process, is then fed as waste water to a drainage system. While the fresh water is passing through the machine in a direction opposite to the direction of movement of the container stock, dirt is absorbed by the cleaning-agent solution and is admixed with the counter-flowing fresh water.
Cleaning machines preferably are designed to be as small as possible and to provide for the highest possible output per hour and thus attain optimal exploitation of the space available for the installation of the machine.
Attempts have been made to reduce the quantity of fresh water and thereby the quantity of waste water used to operate cleaning machines. However, with a reduction of the fresh water quantities on the one hand, but with a faster transit time of the stock to be cleaned on the other hand, there results an increased degree of contamination of the waste water. Moreover, because the use of less water leads to longer persistance of the mixture of cleaning agent and water in the cleaning machine, more time remains for reaction, for example, the precipitation of solids. The equilibrium, which occurs after a certain period of operation of the cleaning machine, between the quantity of fresh water supplied and the quantity of the cleaning agent solution being carried away, necessarily sets itself at a higher level of the salt mass and hence concentration of the mixture, so that the total quantity of the waste water becomes somewhat smaller but its composition less favorable.
When the container stock to be cleaned is transferred from, for example, an alkaline solution in the first water bath, according to experience with the given temperatures and with use of hard water, there occurs a more or less strong petrifaction due to calcification. With inadequate servicing, this fact rapidly leads to faults in the cleaning or rinsing process. It is known that as a result of deposits, heating devices lose their normal facility for heat transmission, vats become encrusted, spray tubes become clogged, and pumps shift in their settings and fall off in performance, etc. All these result in impairment of the cleaning processes.
To prevent or to reduce too extensive precipitation, inhibiting materials, for example complex formers, are frequently added. This procedure, however, does not always successfully achieve operational requirements, when economically tolerable quantities of these chemicals are employed. Moreover, the waste water is thereby additionally contaminated if only to a small extent.
In some cases, softened water is employed to eliminate the risk of precipitation. In this procedure, the salt content of the fresh water is practically unaltered and thus remains in the waste water. The costs of preparation however are particularly high with very hard water.
A genuine saving in fresh water has expectation of success only when the container stock to be cleaned, after being cleaned in the cleaning agent solution and after the first of several stages of rinsing, has the degree of cleanliness of the fresh water supplied to the cleaning machine. This presupposes, however, that, prior to the last washing stage in the cleaning agent and therefore before the addition of fresh water from the main network, relatively clean water is available. If this is not the case, then a larger quantity of fresh water is required to be supplied from the main network for rinsing out the preceding relatively dirty water.
Particularly when the container stock is to be used for foodstuffs, a guaranteed degree of cleanliness in a chemical as well as in a bacteriological respect must be attained. The growth or the possibility of growth of microorganisms can be enhanced with a strong tendency to "fur" formation, hard precipitation, and formation of sediment in the vats and containers of the cleaning machine, which have water applied to them and also in the only sporadically wetted inner parts of the cleaning machines. This requires additional disinfecting means in the stage concerned to keep the germ count in the water or the mixture of water and cleaning agent at a tolerable level.
The waste water of the machine, which flows away enriched with materials and more or less strongly contaminated by being mixed with remnants of cleaning means on rinsing, frequently provokes disturbances in the sewage network, because here strong precipitation depending on composition and time can likewise occur and cause constrictions of the cross-section, clogging and sometimes even complete closing up of the drainage pipes.